Vapor phase methods can be employed to produce particles or thin films. Sputtering, a physical vapor deposition (PVD) technique, is widely used to produce thin films for commercial applications. The method can also be applied to the formation of atom clusters.
A typical sputtering apparatus 10 is shown schematically in FIG. 1A. The apparatus 10 includes a vacuum deposition chamber 12, a planar sputtering target (cathode) 14 and a substrate 16. To sputter deposit a thin film, the sputtering target 14 may be biased with a negative voltage, and an inert gas between the target 14 and the walls of the chamber 12 may be ionized, forming a plasma. Positive ions from the plasma are attracted to the surface of the negatively charged sputtering target 14, where they sputter (eject) atoms from the surface. Electrons are also ejected by ion impact and accelerated to further ionize the gas. Some portion of the ejected atoms are deposited on the substrate 16 to form a thin film. Other material sputtered from the target 14 may be deposited on the walls of the vacuum deposition chamber 12 and lost.
A typical atom cluster generator based on a sputtering process is shown schematically in FIG. 1B. Atom clusters produced in the sputtering chamber 12 at a sufficiently high pressure pass through an aperture in the wall separating the sputtering chamber 12 and the deposition chamber 20. Some portion of the atom clusters are deposited on the substrate 16 facing the cathode 14 to form a cluster deposit or thin film.
Sputtering has been optimized for commercial production of thin films. Sputter deposition is typically carried out in stand-alone vacuum systems with volumes on the order of 1000-10,000 cm3 or more. Magnetically enhanced sputtering (e.g., magnetron sputtering) is widely used to improve sputtering efficiency. Thin film deposition rates may increase by several orders of magnitude when magnets are used to control the path of electrons in the vicinity of the target surface.
It would be advantageous to develop a compact, portable apparatus for the vapor phase production of atom clusters. Ideally, the apparatus would have low material losses and produce clusters efficiently without the use of magnets. It would also be advantageous if the apparatus facilitated in-situ characterization of the generated atom clusters and provided flexible control over the composition of multielement atom clusters. It would be further desirable if the apparatus was scalable for high-volume cluster production.